In many situations it may be necessary to perform an intracranial surgical procedure. By way of example but not limitation, a patient may have suffered a large hemorrhagic stroke and may require accumulated blood to be removed from the interior of the skull so as to relieve pressure on the brain. Or the patient may have developed a tumor which requires removal. Or the patient may have suffered a cerebral injury which requires surgical intervention.
Regardless of the patient's underlying condition and the specific surgical procedure which is to be performed, intracranial surgical procedures typically share a number of common aspects.
For one thing, due to the anatomy involved, intracranial surgical procedures generally require opening the skull at one or more locations, and then accessing specific sites within the interior of the skull in order to effect a desired surgical procedure.
Furthermore, in view of the delicate neurological tissues present in this region of the body, it is often necessary to stabilize the patient's head with some sort of external framework during the surgical procedure. This external framework generally comprises a multi-dimensional frame which is positioned alongside different surfaces of the head, and a plurality of skull pins which extend from the frame into engagement with the skull. By providing the skull pins with sharp distal tips, and by configuring the frame so that the skull pins are directed into the skull from a variety of different angles, the skull can be stabilized during the surgical procedure. See, for example, FIG. 1, which shows a head frame (formed out of stainless steel) offered by Pro Med Instruments GmbH of Freiburg, Germany under the trade name DORO™, and FIG. 2, which shows a skull pin (formed out of a stainless steel pin with a plastic mount) offered by Pro Med Instruments GmbH under the trade name DORO™.
Additionally, since direct visualization is, at best, generally quite limited within the intracranial spaces (e.g., due to the surrounding portions of the skull and, in many cases, the presence of intervening neurological tissues), it is frequently necessary (or, at the very least, highly desirable) to utilize scanners (e.g., X-ray devices, MRI machines, ultrasound imagers, etc.) before, during and after the surgical procedure. Such scanners permit visualization of internal tissue structures even where direct visualization is not possible. In this respect it should be appreciated that the use of such scanners prior to, during and immediately following the surgical procedure can be extremely important in intracranial surgery, due to the restricted fields of view, delicate neurological tissues and navigation requirements. This is particularly true during the intracranial procedure itself. In this respect it should also be appreciated that X-ray devices (e.g., CT machines, C-arm fluoroscopes, etc.) are generally the most desirable type of scanner for use during intracranial surgery, due to the high quality of their images, the ready availability of such devices within the operating suite, etc. MRI scanners are generally not preferred for intraoperative use for a variety of reasons, including the need to remove metal objects from the region of the scanner, etc.
Unfortunately, the need to use these X-ray devices during surgery complicates the design of the aforementioned head frame and skull pins. This is because forming the head frame and skull pins out of stainless steel (the traditional material of choice for operating room frames) dramatically undermines the quality of the X-ray image due to the enormous X-ray signature of stainless steel. See, for example, FIG. 3, which shows a typical X-ray image where no head frame and skull pins are present. Where the head frame and skull pins are formed out of stainless steel, large sections of the X-ray image (i.e., those sections which are aligned with the head frame and/or skull pins) are obscured and hence effectively unusable.
In view of the foregoing, attempts have been made to fabricate the head frame and skull pins out of radiotranslucent materials. Thus, and looking now at FIG. 4, there is shown another system offered by Pro Med Instruments GmbH of Freiburg, Germany under the trade name DORO™, wherein the head frame is made out of carbon graphite (a material which is substantially radiotranslucent) and only the skull pins are made out of stainless steel. As can be seen in FIG. 5, this approach significantly improves the quality of the X-ray images. However, the presence of the stainless steel skull pins in the X-ray field still creates a significant loss of image.
To this end, attempts have been made to fabricate the skull pins out of radiotranslucent materials. Unfortunately, carbon graphite (the material used to fabricate the radiotranslucent head frame) does not provide a satisfactory skull pin, since carbon graphite is too brittle to form the strong, sharp distal tips needed to penetrate into the skull. Attempts to use other radiotranslucent materials (e.g., various plastics) have also proven to be unsatisfactory. As a result, skull pins are frequently formed out of metals (e.g., titanium) which have an X-ray signature which is lower than the X-ray signature of stainless steel. While forming skull pins out of titanium generally results in X-ray images superior to the images formed when using skull pins formed out of stainless steel, there is still substantial image loss due to the X-ray signature of the titanium skull pins. See FIG. 6.
There is, therefore, a substantial need for a new approach for forming skull pins which have all of the strength and integrity needed to effectively penetrate and grip the skull, yet which have a sufficiently small X-ray signature so as to permit the creation of X-ray images of high quality.